Adjective
unrounded (comparative more unrounded, superlative most unrounded)
Not rounded.
Rounded vowels that are front in tongue position are front-central in formant space, while unrounded vowels that are back in articulation are back-central in formant space. Source: Internet
In places where vowels are paired, the right represents a rounded vowel (in which the lips are rounded) while the left is its unrounded counterpart. Source: Internet
In the case of u-umlaut, this entails labialization of unrounded vowels. Source: Internet
Later modifications to his theory allowed for an additional set of eight "secondary Cardinal Vowels" with reverse lip shapes, permitting the representation of eight secondary cardinal vowels (front rounded and back unrounded). Source: Internet
Nonetheless, even in those languages there is usually some phonetic correlation between rounding and backness: front rounded vowels tend to be more front-central than front, and back unrounded vowels tend to be more back-central than back. Source: Internet
Note that some of those diphthongs have been unrounded in several dialects. Source: Internet